The present invention relates to a developing cartridge, and more particularly, to the device having a toner container and a developing chamber and in which a toner agitator is provided in the toner container for agitating toners in a toner container and for transferring the toner to the developing chamber. The present invention also relates to a process cartridge provided with the developing cartridge, and to an image forming device provided with the process cartridge.
There has been provided an image forming device having a developing cartridge which uses a non-magnetic single component type developing agent (hereinafter, simply referred to as xe2x80x9ctonerxe2x80x9d). In such type of the conventional image forming device, in the developing chamber, a toner layer thickness regulation blade is in pressure contact with a developing roller carrying thereon the toner. Thus, a thin toner layer is formed on an outer peripheral surface of the developing roller. The toner of the toner layer is transferred onto a photosensitive body which carries an electrostatic latent image, so that a visible toner image corresponding to the electrostatic latent image is formed. The toner image is then transferred onto a printing sheet, and the toner image on the sheet is fixed.
A printable width in a widthwise direction of the printing sheet is determined by a width of the thin toner layer on the developing roller, the width being in an axial direction of the developing roller, that is, a width of the pressure contact portion between the toner layer thickness regulation blade and the developing roller. Normally, in the conventional developing cartridge, the width of the blade is configured greater than the width of a maximum size printing sheet, and an axial length of the developing roller is greater than the width of the blade.
However, a maximum size printing may not be often performed. Therefore, toner at both axial end portions of the developing roller may not be frequently used, and accordingly, such toner are repeatedly passed through the pressure contact portion under pressure between the blade and the developing roller.
The conventional non-magnetic single component type toner includes base particles and external additives such as silica, alumina and titanium oxide. Due to the repeated pressurization of the toner, the external additives may be embedded into the base particles, and as a result, fluidity of the toner may be degraded, and the degraded toners are stayed at each end portion of the developing chamber. Consequently, imaging quality may be gradually degraded from at widthwise end portions of the printing sheet.
An opening is formed at a boundary between the developing chamber and the toner container positioned beside the developing chamber. A toner transfer member or agitator is rotatably provided in the toner container, and free end of the agitator is protrudable into the opening. Upon rotation of the agitator, toner in the toner container is delivered to the developing chamber through the opening.
In order to avoid long term stay of the toner at the axially end portions of the developing roller, proposed is a developing cartridge in which a width of the opening is made approximately equal to the width of the developing chamber, so that the width of the opening is equal to or greater than the printable width, and a length of the agitator (the length being extending in the widthwise direction of the printing sheet) is made substantially equal to the width of the opening.
However, with this arrangement, even though the toner circulation occurs in a direction of an array of the developing chamber and the toner container. However, toner circulation along the axial direction of the developing roller, i.e., in the widthwise direction of the developing chamber may not easily occur. Therefore, it would be impossible to prevent the toner at the axially end portions of the developing roller from being stayed or rested thereat and degraded.
In case where the width of the opening is made equal to the printable width, if the toner is not uniformly delivered to the developing chamber in the widthwise direction of the opening, toner may not be sufficiently supplied onto the developing roller, and a variation in image density may occur such as formation of linear scratches extending in the longitudinal direction of the printing sheet at the toner shortage area of the developing roller.
In order to avoid this problem, provision of an additional agitator in the developing chamber may be conceivable. With such an arrangement, toner circulation in the developing chamber in the widthwise direction thereof can be improved so as to avoid stay of toner at each end portion of the developing chamber. However, additional driving system is required for driving a additional agitator, and intricate structure results, and production cost may be increased.
Another proposal is made in which a lower end of the opening is lowered, i.e., an upper end of a partitioning wall is lowered, the partitioning wall partitioning the toner container from the developing chamber in order to promote toner circulation between the toner container and the developing chamber. That is, the toner delivered from the toner container into the developing chamber can be returned back to the toner container because of own gravity of the toner because of a low level damming of the partitioning wall. However, with this structure, toner delivering amount to the developing roller may be decreased, and a fogging may occur in the printed image if a large area printing is performed.
Still another proposal is made in which the agitator in the toner container is formed of a highly flexible thick PET sheet to forcibly push the toner in the toner container to the developing chamber in order to greatly enhance toner transferring efficiency to the developing chamber. After the agitator is moved past the opening, the forcibly delivered toner into the developing chamber can be easily returned back to the toner container because greater amount of toner has been supplied into the developing chamber. However, with this structure, loud noise is generated when the deformation of the PET sheet is released, for example, when the deformed PET sheet passes through the opening.
It is therefore, an object of the present invention to overcome the above described drawbacks and to provide an improved developing cartridge capable of providing sufficient toner circulation in the widthwise direction of the developing chamber with a simple construction and without decreasing toner transferring amount to the developing roller and without generation of noise.
Another object of the invention is to provide a process cartridge having the above developing cartridge, and to provide an image forming device incorporating therein the process cartridge.
These and other object of the present invention will be attained by providing a developing cartridge including a developing housing, a developing agent container, and an improved developing agent agitating and transferring member. The developing agent container holds therein a developing agent. The developing agent container is connected to and positioned beside the developing housing and is formed with an opening in communication with the developing housing. The opening has a length in a widthwise direction of an image recording sheet. The developing agent agitating and transferring member is rotatably disposed in the developing agent container about a rotation axis for agitating the developing agent in the developing agent container and transferring the developing agent to the developing housing. The developing agent agitating and transferring member includes circulation means for circulating the toner in the developing housing in the widthwise direction thereof.
In one preferred fashion, the circulation means includes means for promoting a transferring efficiency of the developing agent from the developing agent container to the developing housing at a lengthwise center portion of the opening higher than the efficiency at lengthwise end portions of the opening. The developing agent agitating and transfer means includes a first blade rotatable about the rotation axis and having a length equal to or greater than the length of the opening and positioned in alignment with the opening. The promoting means includes a second blade also rotatable about the rotation axis and having a length smaller than the length of the first blade and positioned at the lengthwise center of the opening.
In another preferred fashion, the developing agent agitating and transferring member includes a center shaft, a support member and a flexible blade. The center shaft is rotatable about its axis and is provided in the developing agent container and extends in the widthwise direction of the image recording sheet. The support member is fixed to the center shaft and extends in the widthwise direction of the image recording sheet. The flexible blade has a base end fixed to the support member and a free end in flexible deforming contact with an inner surface of the developing agent container. The flexible blade serves as the circulation means and comprises end blade sections and an intermediate blade section. The end blade sections each has a base end fixed to each longitudinal end of the support member, and has free end in flexible deforming contact with the inner surface of the developing agent container. Each free end is slanted with respect to the support member in such a manner that a radial length between the base end and the free end is gradually increased from a longitudinal end toward a longitudinal center of the support member. The intermediate blade section is positioned between the end blade sections and has a base end fixed to the support member and a free end. Each end section has a maximum radial length at a side closest to the intermediate blade section. The intermediate section has a radial length between the base end and the free end smaller than the maximum radial length.
In another aspect of the present invention, there is provided a process cartridge including a casing, an electrostatic latent image carrying member disposed in the casing, and the above described developing cartridge. The developing cartridge is detachable with respect to the casing.
In still another aspect of the invention, there is provided an image forming device including the above described process cartridge.